Dynamic stability and buckling of viscoelastic plates and nanobeams subjected to distributed axial forces.

Doctor of Philosophy in Mechanical Engineering. University of KwaZulu-Natal, Durban 2016.Plates and beams are typical examples of structures that must be analyzed and understood. Buckling and vibration represent for such structures a potential source of fatigue and damage. Damage and fatigue are often caused by axial forces. The current research uses differential quadrature method to study the stability of viscoelastic plate subjected to follower forces in one hand, and the Rayleigh-Ritz method to analyze the buckling of Carbone nanotubes subjected to point and axial load in other hand. For plate, the 3D relation of viscoelastic is used to derive the equation of vibration of viscoelastic rectangular plate subjected to follower force. This equation is solved numerically by differential quadrature method, then the dynamic stability analysis is done by plotting the eigenvalues versus the follower force. We employ the Euler Bernoulli beam theory and the nonlocal theory to derive the equation of equilibrium of Carbone nanotubes subjected to point and axial loads. Rayleigh-Ritz method is used to calculate buckling loads, and the effects of equation's parameters on that buckling loads are analysed properly. Frequencies of vibration of viscoelastic plates and critical load obtained by using differential quadrature method are compared to other results with good satisfaction. The same satisfaction is observed when the buckling load values of Carbone nanotubes obtained using the Rayleigh-Ritz methods are compared to those existing in the literature. The cantilever viscoelastic plate undergoes flutter instability only and the delay time appears to influence that instability more than other parameters. The SFSF plate undergoes divergence instability only. The both types of instability are observed CSCS plate subjected to uniformly follower load but the flutter instability disappears in presence of triangular follower load. The values of the mentioned critical loads increase with triangular follower load for all boundary conditions. The aspect ratio has a large influence on the divergence and flutter critical load values and little influence on the instability quality. The laminar friction coefficient of the flowing fluid increases the critical fluid velocity but its effect on the stability of viscoelastic plate behavior is minor. The nonlocal parameter appears to decrease buckling load considerably. Buckling is more sensitive to the magnitude of the tip load for the clamped-free boundary conditions. The application of the present theory to a non-uniform nanocone shows that the buckling loads increases with radius ratio and decreases with small scale constants

Yarı Rijit Bağlı Betonarme Bacaların Serbest Titreşiminin Diferansiyel Transformasyon Metodu İle Analizi

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2015Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2015Bu çalışmada; Timoshenko kiriş teorisi dikkate alınarak, yarı rijit bağlı betonarme bacaların serbest titreşim analizi incelenmiştir. Farklı zemin kayma modülleri için çökmeye ve dönmeye karşı elastik yaylar kullanılarak modellenen sabit enkesitli betonarme bacaların ilk üç modlarına ait doğal açısal frekansları, analitik metotla ve Diferansiyel Transformasyon Metodu (DTM) kullanılarak elde edilmiştir. Tüm analizlerde analitik yöntem ve DTM’nin yanında SAP2000 programı da kullanılmıştır. Sistemlerde kullanılan çökme ve dönme yayı rijitlikleri ASCE 4-98 yönetmeliği kapsamında zemine ait kayma modülüne, poisson oranına ve baca temelinin yarıçapına bağlı olarak hesaplanmıştır. DTM’den elde edilen sonuçların analitik yöntemle elde edilen sonuçlara oldukça başarılı bir şekilde yakınsadığı görülmüştür. Yarı rijit bağlı sistem için elde edilen açısal frekans değerleri, ankastre mesnetli sistem ile kıyaslanmıştır. Analizler sonucu elde edilen açısal frekans değerleri tablo halinde verilmiştir. İlk üç moda ait mod şekilleri ve normalize edilmiş eğilme momenti diyagramları sunulmuştur.In this study, the free vibration analysis of semi-rigid connected reinforced concrete chimneys is investigated. The first three natural circular frequencies of the chimneys which have uniform cross sections along their heights and modeled by using different translational and rotational springs due to different soil conditions, are obtained using analytical solution and Differential Transform Method (DTM). SAP2000 is used in addition to analytical solutions and DTM solutions in numerical analysis. The stiffnesses of elastic springs that are used in numerical analysis are calculated by means of shear modulus of the soil, poisson ratio of the soil and radius of the foundation in accordance with ASCE 4-98. The results obtained from DTM are compared with the results of the analytical solution and very good proximity is observed. The natural frequencies of semi-rigid systems are compared with the natural frequencies of clamped foundation system. The natural frequencies are tabulated. After all, the mod shapes and normalized bending moment diagrams are presented

A Numerical and Experimental Investigation of a Special Type of Floating-Slab Tracks

This thesis presents a research study on the dynamic behavior of a special type of FST used in recently built subway system in Doha, Qatar. The special FST has a continuous concrete slab with periodic grooves for which the track can be modeled as periodic structure with a slab unit having two elements with different cross sections. Extensive numerical and experimental investigations were conducted on a multi-unit full-scale mockup track. The numerical investigations were carried out using both a fast running model based on the Dynamic Stiffness Method and a detailed Finite Element model. In the experimental campaign, experimental vibration test was performed to identify the actual vibration response of the mockup track. Results from the experimental investigations were then used for verifying the numerical models and carrying out a model updating exercise for the fast running model. The model updating process was carried out according to an automated hybrid optimization approach. Finally, the updated model was extended to an infinite model and used in a parametric study to investigate the influence of varying groove’s thickness on the dynamic behavior of the special track with infinite length for both bending and torsion scenarios. The parametric study suggested that reducing the thickness below 50% of the full thickness of the slab significantly affects the dynamic behavior of the special FST

On The Dynamic Stability of Functionally Graded Material Beams Under Parametric Excitation

The dynamic stability of functionally graded material (FGM) beams subjected to parametric excitation is studied using finite element method. First order shear deformation theory (Timoshenko beam theory) is used for the analysis of the beams. The shape functions for the beam element are established from the differential equation of static equilibrium. Floquet’s theory is used to establish the stability boundaries. A steel-alumina functionally graded ordinary (FGO) beam with steel-rich bottom is considered for the analysis. For the analysis of functionally graded sandwich (FGSW) beam, alumina and steel are chosen as top and bottom skin respectively and the core is FGM with steel and alumina as constituent phases. The material properties in the direction of thickness of FGM are assumed to vary as per power law and exponential law. The effect of property distribution laws on critical buckling load, natural frequencies and parametric instability of the beams is investigated. Also, the effect of variation of power law index on the critical buckling load, natural frequencies and dynamic stability of beams is determined. It is found that the property variation as per exponential law ensures better dynamic stability than property variation as per power law. Increase in the value of power law index is found to have detrimental effect on the dynamic stability of the beams. Influence of the elastic foundations on the dynamic stability of the beams is studied. Pasternak elastic foundation is found to have more enhancing effect on the dynamic stability of the beam than Winkler elastic foundation. The dynamic stability of FGO and FGSW beams used in high temperature environment is investigated. It is observed that increase in environmental temperature has an enhancing effect on the instability of the beams. The effect of beam geometry, rotary inertia, hub radius and rotational speed on natural frequencies as well as on the parametric instability of rotating FGO and FGSW cantilever beams is studied. It is observed that increase in rotational speed enhances the dynamic stability of the beams. Parametric instability of a pre-twisted FGO cantilever beam is investigated. The effect of property distribution laws and pre-twist angle on critical buckling load, natural frequencies and parametric instability of the beam is studied. The increase in the value of power law index is found to have enhancing effect on the parametric instability of the beam. The increase in pre-twisting of the beam reduces the chance of parametric instability of the beam with respect to the first principal instability region. But the increase in pre-twist angle has a detrimental effect on the stability of the beam for second principal instability region

Dynamic response of thin-walled composite structures with application to aircraft wings

A general analytical method is developed to study first the buckling behaviour and then the dynamic characteristics of thin-walled composite structures with the presence of bending torsion coupling. The dynamic response theory incorporates the dynamic stiffness matrix approach and generalised coordinates using the normal mode method. Structural components considered are thin-walled laminated composite beams with carbon-fibre, glass-fibre or other reinforced plastic lay-ups. The examples of such beams and their applications include aircraft wings, hulls of ships, helicopter and wind turbine blades. All assumptions made in this work are based on elastic linear small deflection beam theory so that the overall response of the beam is represented by the superposition of all individual responses in each mode. Bending-torsion coupling effects arising from the anisotropic nature of fibrous composites, as well as due to non-coincident centroid and geometric shear centre of the beam crosssection, are the main contributory elements when developing the theory. The beam is subjected to time dependent forces and/or torques which can be either concentrated or distributed over its length. Both deterministic and random loads are considered. An important example of a deterministic load is one that varies harmonically in time. The Duhamel integral is employed to calculate the response to any arbitrary time dependent deterministic load. The random load is assumed to be Gaussian, having both stationary and ergodic properties. The evaluation of the response to the random load is carried out in the frequency domain by relating the Power Spectral Density (PSD) of the output to that of the input using the complex frequency response function. A number of PSD distributions are considered as random input in order to determine the PSD of the dynamic response. Atmospheric turbulence, which is considered to be one of the forms of random excitation, is modelled using the von Karman spectra for composite aircraft wings. In order to establish the methodology, bending-torsion coupled metallic beams are first ,investigated. The bending-torsion coupling in such beams occurs due to non-coincident centroid and geometric shear centre of the beam cross-section. The natural frequencies and mode shapes in undamped free vibration are obtained and the significance of generalised ,mass in each of the modes of vibration is evaluated. A normal mode method is then used to compute the frequency response function of the beam. The effects of shear deformation rotatory inertia and axial load on the frequencies, mode shapes and dynamic response characteristics are demonstrated. It was essential at an earlier stage of the investigation to validate the chosen composite beam modelling. Among all the different techniques used to determine the rigidities of a composite beam, the buckling load provides a reasonable estimate. The elastic critical buckling loads of thin-walled laminated composite columns for various end conditions are established theoretically using the exact stiffness method. The effect of shear deformation on the buckling characteristics of the column is demonstrated. Experiments are carried out to establish the elastic critical buckling load of metallic and laminated composite columns. Theoretical predictions of the buckling behaviour are corroborated by experimental results and other published results. The investigation is then focused on composite beams, but the response analysis of such beams is significantly more complicated than that of their metallic counterparts. This is mainly due to anisotropic characteristics of laminated fibrous composites. A detailed parametric study with the variation of significant composite parameters, such as ply angle, is undertaken and the importance of the results are highlighted. A suite of computer programs in FORTRAN is developed to predict the bucklingbehaviour, the free vibration and the responsec characteristics of thin-walled composite or metallic beams based on the theory proposed. Numerical results are presented, fully discussed and commented on

Advances in Vibration Analysis Research

Vibrations are extremely important in all areas of human activities, for all sciences, technologies and industrial applications. Sometimes these Vibrations are useful but other times they are undesirable. In any case, understanding and analysis of vibrations are crucial. This book reports on the state of the art research and development findings on this very broad matter through 22 original and innovative research studies exhibiting various investigation directions. The present book is a result of contributions of experts from international scientific community working in different aspects of vibration analysis. The text is addressed not only to researchers, but also to professional engineers, students and other experts in a variety of disciplines, both academic and industrial seeking to gain a better understanding of what has been done in the field recently, and what kind of open problems are in this area

Dynamic Analysis Of Adaptive Aircraft Wings Modelled As Thin-walled Composite Beams

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2015Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2015Akıllı veya uyarlanabilir malzeme sistemleri teknolojilerinin geliştirilmesine gittikçe büyümekte olan bir ilgi gözlenmektedir. Bu ilginin en büyük sebebi bu tarz malzemelerin havacılık ve uzay, otomotiv, helikopter ve turbomakinelerin palleri ve robot kolları gibi çeşitli farklı yapılara kolayca uyarlanabilmesi ve kullanılabilir durumda olmasından kaynaklanmaktadır. Akıllı veya uyarlanabilir malzemelerin kullanımı ile, yapıların dinamik karakteristiklerinin öngörülebilir bir şekilde kontrol edilmesi mümkündür. Bu kontrol sayesinde yapısal rezonans ve çırpınma gibi bir takım dinamik kararsızlıkların önüne kolaylıkla geçilebilir. Yapılmış olan bu tez çalışmasında, uçak kanatlarının dinamik davranışları incelenmiş ve piezoelektrik eyleyiciler yardımı ile doğal frekansların kontrolü sağlanmıştır. Bu tez boyunca iki farklı model kullanılmıştır. Bunlar sırasıyla Timoshenko kiriş ve ince cidarlı kompozit kiriş modelidir. Her iki model için de yapıların doğal frekansları hesaplanmış ve daha sonrasında akıllı malzemelerin yardımıyla doğal frekansların kontrolü sağlanarak, değişimleri incelenmiştir. Ayrıca yapının dinamik cevabı da farklı kontrol yasaları altında incelenmiştir. İlk olarak, ince cidarlı kompozit kiriş teorisi tanıtılmıştır. Verilen formülasyon birincil ve ikincil çarpılma etkilerini içermektedir. Ayrıca bu kiriş modeli bir takım klasik olmayan etkileri de formülasyonunda barındırmaktadır. Bu klasik olmayan etkiler kısaca malzeme eşyönsüzlüğü, enlemesine kayma deformasyonu ve çarpılma kısıtlamasıdır. Diğer taraftan, ince cidarlı kompozit kirişlerin yönlülüğü, geniş bir elastik bağlaşım meydana getirmektedir. Bu bağlamda temel denklemler ve enerji ifadeleri verilmiştir. Daha sonrasında ise Hamilton Prensibi aracılığıyla genel hareket denklemlerinin eldesi gerçekleştirilmiştir. Daha sonra serbest titreşim problemi açıklanmıştır. Bu problemi incelerken iki farklı kompozit konfigürasyonundan bahsedilmiş ve antisimetrik konfigürasyon, başka bir deyişle Circumferentially Uniform Stifness (CUS) konfigürasyonu kullanılarak  dikey-yatay eğilme ve enlemesine kayma bağlaşımlı hareket denklemleri elde edilmiştir. Ayrıca, sırasıyla kayma etkilerini içeren ve içermeyen iki farklı teoriden bahsedilmiştir. Bu teoriler Shearable ve Unshearable Theory olarak literatürde bulunmaktadırlar. Serbest titreşim problemi hareket denklemlerine bir çözüm elde etmek için sayısal bir yöntem kullanılmıştır. Denklemlerin karmaşıklığı ve bağlaşımlı olması analitik bir çözüm elde edilmesini imkansız kılmaktadır. Kullanılan sayısal yöntem Extended Galerkin Method olarak bilinmektedir ve bu kısımda açıklanmıştır. Bu metod, hareket denklemlerini ayrıklaştırmakta ve bunu şekil fonksiyonları önererek gerçekleştirmektedir. İfadeler, şekil fonksiyonları ve genelleştirilmiş koordinatların çarpımı olarak tanımlanmaktadır. Bu yöntemin diğer sayısal yöntemlere göre üstünlüğü ise, önermiş olduğu şekil fonksiyonunun sadece geometrik sınır şartlarını sağlamasının yeterliliğidir. Bu yöntemle hareket denklemleri çözülmüş ve doğal frekanslar elde edilmiştir. Kanat elmas kesite sahip olacak şekilde modellenmeden önce oluşturulan matematik modelin doğruluğunu test etmek amacıyla referans kitaptan alınan sayısal bir örnek çözülmüştür. Çözülen bu örnek için elde edilen sonuçlar ve referans kitapta verilen sonuçlar karşılaştırılmıştır. Karşılaştırma sonucunda Extended Galerkin Metodu ile elde edilen sonuçlar ile kitap tarafından verilmiş olan sonuçların birbiriyle çok iyi bir uyum içerisinde olduğu görülmüştür. Böylece geliştirilmiş olan matematik modelin doğruluğu kanıtlanmıştır. Daha sonrasında kanat ince cidarlı kompozit kiriş olarak modellenmiştir. Serbest titreşim bölümünün sonucu olarak ise uçak kanatları için titreşim kontrolü yokluğunda doğal frekanslar elde edilmiştir. Devamında aktif titreşim kontrolü konsepti, yapısal karakteristikler üzerinde bir kontrol sağlanması amacıyla sisteme eklenmiştir. Aktif kontrol tanımı verilmiş,piezoelektrik malzemeler tarafından indüklenen momentlerden bahsedilmiş ve sınır momenti hakkında detaylı bilgi verilmiştir. Ayrıca, uygulanmış olan iki farklı kontrol yasasından bahsedilmiştir. Bunlar sırasıyla ortantısal geribesleme kontrol yasası ve hıza bağlı geribesleme yasası olarak adlandırılmaktadırlar. Aktif kontrolün sisteme katılması ile çözüm yönteminde modifikasyonlar yapılacağından durum uzay gösterimi anlatılmış ve sonuçlar elde edilmiştir.  Aktif geribesleme kontrolü uyarlanabilir malzemeler aracılığıyla sağlanmıştır. Piezoelektrik katmanlar ana yapının içerisine simetrik bir şekilde gömülmüş ve piezoelektrik eyleyiciler tüm kiriş uzunluğu boyunca yayılmıştır. Bunun sonucu olarak, kirişin uç noktasında bir sınır momenti indüklenmiş ve bunlar hareket denklemlerini etkilemek yerine sınır şartlarında tekil moment ifadeleri olarak yer almışlardır. Orantısal ve hıza bağlı geribesleme kontrol yöntemleri kullanılmış ve elyaf açısı dağılımının temel frekanslar üzerindeki etkisi incelenmiştir. Doğal frekanslar elde edilirken kütle ve katılık matrislerine piezoelektrik katmanların etkisi de eklenmiştir. Bu etkinin ihmal edildiği durum için de analizler yapılmış ve sonuçlar karşılaştırıldığında doğal frekanslarda yaklaşık olarak \%5'lik bir fark ortaya çıkmıştır. Literatürdeki çoğu çalışmalarda bu etkiler ihmal edilirken, yapılan bu tez çalışmasında bu etkinin önemine de vurgu yapılmıştır. Son olarak, piezoelektrik etkileri iyice algılamak ve anlamak amacıyla Timoshenko kiriş teorisini içeren bir örnek çalışma göz önüne alınmış ve orantısal geribesleme kontrol yasası uygulanarak doğal frekanslar bu örnek kiriş için elde edilmişlerdir. Bu örneğin hareket denklemleri ince cidarlı kiriş modelindeki denkemler kadar zor olmadığından analitik bir çözüm elde etmek mümkün olmuştur. Analitik yöntemin yanısıra, problem yarı-analitik yöntem olan Differential Transform Method (DTM) ve Extended Galerkin Method (EGM) ile tekrar çözülmüştür. Elde edilen sonuçlar ilgili yerlerde tablo halinde verilmiştir. Bir sonraki adımda ise, uçak kanadımız artık elmas kesitli ince cidarlı kiriş olarak ele alınarak üzerine kontrol yasaları uygulanmıştır. Değişen kontrol kazançları ile doğal frekanslar elde edilmiş ve grafik olarak gösterilmişlerdir. Daha sonra modeli daha iyi analiz etmek amacıyla uzunluk ve narinlik oranı gibi parametreler değiştirilerek doğal frekansların incelendiği çalışma yapılmıştır, sonuçlar grafik üzerinde gösterilmişlerdir. Optimal kontrol yasası tanıtılmış ve yapıya uygulanması gerçeklenmiştir. Ayrıca, kiriş ucuna uygulanan Dirac Delta impulsu altında yapının dinamik cevabı incelenmiş, çeşitli kontrol yasaları için karşılaştırma yapılmıştır. Sonuç olarak, elmas şeklinde ara kesite sahip olan ince cidarlı kompozit uçak kanadı için, aktif titreşim kontrolü akıllı malzemeler aracılığıyla sağlanmıştır. Piezoelektrik malzemeler kapalı devre geribesleme kontrol sistemini sağlamak amacıyla algılayıcı ve eyleyici olarak kullanılmışlardır. Gelecek çalışmalarda ise yapının dışarıdan gelecek olan kuvvetlere vereceği cevabın incelenmesi ve kontrolünün sağlanması gerçekleştirilecektir.There has been a growing interest in the development of the smart material systems technology due to their incorporation in various structures ranging from aeronautical/aerospace, automotive, helicopter and turbo-machinery rotor blades, robot manipulators. Using adaptive materials, the dynamical characteristics of the structure could be controlled in a predictable manner to avoid the dynamical instabilities such as structural resonances.  In this thesis, dynamic behaviour of aircraft wings is investigated and control of natural frequencies is achieved using piezoelectric actuation. Two different models namely, Timoshenko beam and thin-walled composite beam are used in this study. Natural frequencies of both model are obtained and using active control their variations are examined. First, thin walled composite beam theory is introduced with detailed formulation including the effects of primary and secondary warping. This beam model also incorporates a number of non-classical effects such as material anisotropy, transverse shear deformation and warping restraint. Moreover, the directionality property of thin-walled composite beams produces a wide range of elastic couplings. In this respect, constitutive equations and energy expressions are given. Equations of motion are derived using Hamilton principle. Second, in order to determine natural frequencies without piezoelectric influence, free vibration problem is formulated for an anti-symmetric lay-up configuration, also referred as Circumferentially Uniform Stiffness (CUS). Due to the anti-symmetry in lay-ups this configuration generates the coupled motion of transverse-lateral bending-shear. The equations of motion are discretized using Extended Glaerkin Method (EGM) to determine the natural frequencies of the system. The effect of transverse shear on the natural frequencies is also investigated by simply including and excluding transverse shear in the free vibration analyses, which has found to be significant for higher modes.   For validation purposes, analyses are conducted for a box beam thin walled composite beam and results are compared with the literature. Then, the analyses are repeated for a diamond shaped cross-section  section and the results of different cross-sections are compared and discussed. Active vibration control is introduced to gain an ability to control dynamic characteristics of structures. Implementation of piezoelectrically induced moments regarding the boundary moment is explained and two different control laws, namely proportional and velocity feedback control laws and their effects are investigated. The equations of motion that includes the effect of piezoelectric layers are cast into the state-space representation to obtain the dynamic response of the beam. Before analyzing thin-walled composite beams, a numerical example is solved to attain a deeper understanding about the effect of piezoelectric materials on the natural frequencies. This beam model is developed using the first order shear deformable theory (Timoshenko beam theory) and then solved to determine the natural frequencies with and without piezoelectric layers influence for various boundary conditions and lay-ups. Next, the similar analyses are also carried for thin walled composite beams highlighting the effects of piezoelectric layers, material anisotropy and transverse shear on the natural frequencies for varying feedback gains. Besides, several control laws such as proportional feedback gain and velocity feedback gain are used for vibration control and their results are compared. In addition, optimal control law is implemented and dynamic response of the structure is investigated using different control laws. In conclusion, for a diamond shaped thin-walled composite aircraft wing, active vibration control is achieved using adaptive materials. Piezoelectric materials are used as sensors and actuators to provide closed-loop feedback control system. In future studies, response of the structure to the external forces will be investigated and controlled by using adaptive materials.Yüksek LisansM.Sc

Research in Structures, Structural Dynamics and Materials, 1990

The Structural Dynamics and Materials (SDM) Conference was held on April 2 to 4, 1990 in Long Beach, California. This publication is a compilation of presentations of the work-in-progress sessions and does not contain papers from the regular sessions since those papers are published by AIAA in the conference proceedings

Vibration analysis of damped complex structures

Imperial Users onl

Micro - and macro - mechanical properties of aerospace composite structures and their dynamic behaviour

The research presented in this thesis focuses on the micro- and macro-mechanical properties of aerospace composite structures, and their buckling, free vibration, and flutter behaviour. The first part of the thesis concentrates on fundamental experimental research into prediction and enrichment of polymers composites with nanoparticles with particular emphasis on polyurethane and polyaniline. To this end, a conducting thermoplastic elastomer is developed and characterised using physiochemical methods for thermo-mechanical properties. Consequently, a sophisticated new polyurethane nanocomposite elastomer with improved mechanical and thermal properties is developed. The second part of the thesis is a development of an accurate dynamic stiffness matrix for a three-layered sandwich beam of asymmetric cross-section using the Timoshenko beam theory, Hamiltonian mechanics and symbolic computation. The resulting dynamic stiffness matrix is used to investigate the free vibration characteristics of a number of sandwich beams examples and their results are validated by experiment. Next, a detailed analysis is carried out to establish the rigidity properties (stiffnesses) of fibre reinforced composite structures with particular emphasis on solid rectangular and thin-walled box section. The effect of ply orientation on rigidity properties and the consequent coupling between various modes of deformation is studied. Buckling analysis is carried out to provide an estimate of the stiffnesses. Free vibration investigations on flat and box carbon fibre-reinforced composite beams are then carried out to gain important insights into the material- geometrical coupling effects, and modal interchange in bending-torsion coupled behaviour. Although the dynamic stiffness method is primarily used in the analyses, some complementary finite element analysis and experimental modal analysis using an Impulse Hammer Kit were performed to confirm the predictable accuracy of the dynamic stiffness method. A few carefully designed composite beams were fabricated for the experimental work. Flutter behaviour of swept and unswept wing is also investigated. The results are discussed with significant conclusions drawn. A scope for further work is outlined